Evidence for an Effect of Fetal Growth on the Risk of Tuberculosis

12 Jan 2010

Paul Chinnock

Source: Journal of Infectious Diseases (see original article or PDF)

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Citation: Villamor E, Iliadou A, Cnattingius S. Evidence for an Effect of Fetal Growth on the Risk of Tuberculosis. J Infect Dis: 202(3):409-413.

Tuberculosis is a major global health concern, with over 13 million active cases and around 1.3 million deaths every year. Amongst diseases of infectious origin it is ranked fourth in terms of disease burden (after pneumonia, diarrhoeal disease and AIDS). But it is perhaps surprising that the disease is not more common, because a far greater number of people (perhaps one third of the world’s population) are infected with the disease agent, Mycobacterium tuberculosis, but have not developed the disease itself. There is increasing interest in identifying the factors that make a person more likely to suffer from TB disease.

A study conducted in Sweden has examined the relationship between TB and birth weight. In a cohort study, researchers used data from 21,596 twins born between 1926 and 1958. There were only 256 cases of TB, Sweden having low rates of the disease. The incidence of tuberculosis was inversely related to birth weight and to the ponderal index. (The latter measure is birth weight in grams multiplied by 100 and divided by the cube of birth length in centimetres.) Every 500g of birth weight was associated with an 11% lower risk of TB, and every 0.2 of ponderal index was associated with an 8% risk reduction. The associations were stronger in men than in women.

Amongst those monozygotic (“identical”) twins where one individual developed TB and the other did not, the TB risk was 46% lower for every 500g of birth weight. As associations among monozygotic twins are largely independent of shared genetic or environmental factors, the authors postulate that fetal growth may play a causal role in susceptibility to TB, possibly through early programming of the immune system.

The nutrition of mothers during pregnancy is a key factor determining fetal growth rate and thus birth weight. Poor maternal nutrition could thus be influential in TB susceptibility.

It has of course long been established that low birth weight (usually taken as meaning below 2.5kg) is a major determinant of mortality, morbidity and disability in infancy and childhood and also has a long-term impact on health in adult life. Some 30 million low-birth-weight babies are born annually (23.8% of all births), most of them in developing countries where TB rates are also highest.

It would be interesting to know whether, in the developing world, low-birth-weight babies are highly susceptible to TB. Unfortunately health information systems in developing countries are such that an analysis of data as performed in the Swedish study is unlikely to be possible. Nevertheless, this study reinforces the view that a mother’s nutrition is crucial for the health of her child. Nutrition programmes could play a part in helping to reduce the number of cases of TB in the world’s poorest countries.

Note: Unfortunately, this research is published in a journal which is not open access. To see the full article, therefore, a subscription to the Journal of Infectious Diseases is necessary. In some developing countries, access may be possible through HINARI.

2010 The Infectious Diseases Society of America